Excel VBA - Append .xls to filename to open file - vba

Question

I have code to open a file with a variable date, as shown below. This code will not work without entering m.d.y.xls into the input box. I want to only have to enter m.d.y into the input box. Please take a look and let me know what I am missing. Thanks!
Dim wbkOpen As Workbook
Dim strFilePath As String
Dim strFileName As String
strFilePath = "D:\Users\stefan.bagnato\Desktop\Daily Performance Summary\Agent Group Daily Summary "
strFileName = InputBox("Enter last Friday's date in the format M.D.Y", "Friday's Date")
Set wbkOpen = Workbooks.Open(strFilePath & strFileName, False, True)

Answer 1

This is basic string concatentation:
strFilePath & strFileName & ".xls"
You should probably check to ensure the file exists, otherwise there will be an error:
Dim fullFileName As String
strFilePath & strFileName & ".xls"
If Dir(fullFileName) = "" Then
MsgBox "Invalid filename!"
Exit Sub
End If
Set wbkOpen = Workbooks.Open(fullFileName, False, True)
Ideally, you can avoid user-input (which is prone to error) altogether:
Const strFilePath As String = "D:\Users\stefan.bagnato\Desktop\Daily Performance Summary\Agent Group Daily Summary "
Dim wbkOpen As Workbook
Dim LastFridayDate As String
Dim fullFileName As String
Dim fdlg as FileDialog
LastFridayDate = Format(Date - (Weekday(Date, vbFriday) - 1), "m.d.yy")
fullFileName = strFilePath & LastFridayDate & ".xls"
If Dir(fullFileName) = "" Then
If MsgBox("The file named " & fullFileName & " doesn't exist. Would you like to manually locate the file?", vbYesNo) = vbNo Then
Exit Sub
Else
Set fdlg = Application.FileDialog(msoFileDialogOpen)
'## Opens the fileDialog in the normal folder where these files should exist
fdlg.InitialFileName = strFilePath
'## Display the fileDialog to the user
fdlg.Show
'## Validate the fileDialog hasn't been canceled
If fdlg.SelectedItems.Count <> 0 Then
'## Return the value of the item selected by the user
fullFileName = fdlg.SelectedItems(1)
Else:
MsgBox "No file selected, exiting procedure..."
End If
End If
End If
Set wbkOpen = Workbooks.Open(fullFileName, False, True)
Of course allowing the user to manually select the file may ultimately require additional validation and/or error-handling (i.e., what if they select the wrong file? How can the program know which date is the correct date [I'd wager that it can't, without doing an ugly brute force loop which still makes a lot of assumptions which might not always hold] What if they select a PDF or a PPT file instead of an XLS, etc. but those points are entirely out of scope for this question.)
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